The present invention relates in general to the field of hologram production and display and, more particularly, to a system and method for providing multiple and full color holographic stereograms.
One-step hologram (including holographic stereogram) production technology has been used to satisfactorily record holograms without the traditional step of creating preliminary holograms. Both computer image holograms and non-computer image holograms may be produced by such one-step technology. In some one-step systems, computer processed images of objects or computer models of objects allow the respective system to build a hologram from a number of contiguous, small, elemental pieces known as elemental holograms or hogels. To record each hogel on holographic recording material, an object beam is conditioned through the rendered image and interfered with by a reference beam. Examples of techniques for one-step hologram production can be found in the U.S. patent application entitled xe2x80x9cMethod and Apparatus for Recording One-Step, Full-Color, Full-Parallax, Holographic Stereograms,xe2x80x9d Ser. No. 09/098,581, naming Michael A. Klug, Mark E. Holzbach, and Alejandro J. Ferdman as inventors, and filed on Jun. 17, 1998, which is hereby incorporated by reference herein in its entirety.
Many holographic stereogram recording systems, and horizontal parallax-only one-step holographic stereogram recording systems in particular, generally require highly specialized optics in order to condition and modulate laser light to encode image information. In a standard optical system of this type, laser light directed through or reflected from a spatial light modulator (SLM) usually proceeds through a number of cylindrical lenses that serve to produce a magnified, anamorphic image of the SLM at the front focal plane of an output cylindrical lens, typically a fast cylindrical lens (FCL) which is often defined as a cylindrical lens with an effective f number less than 1.0. Examples of techniques for horizontal parallax-only one-step holographic stereogram production can be found in the U.S. patent application entitled xe2x80x9cSystem and Method for Producing and Displaying a One-Step, Edge-Lit Hologram,xe2x80x9d Ser. No. 09/504,730, naming Michael A. Klug and Mark E. Holzbach as inventors, and filed on Feb. 16, 2000, which is hereby incorporated by reference herein in its entirety.
Anamorphic image relay is often required to match the aspect ratio of the fast cylindrical lens to that of the spatial light modulator. The high cost, and relatively large degree of aberration characteristic of large cylindrical lenses, suggests adapting the anamorphic projection system for use with a fast cylindrical lens where one dimension (e.g., the xe2x80x9cpowerxe2x80x9d dimension) is reduced in size. Also, the lenses needed for anamorphic relay are by necessity cylindrical themselves. Such lenses are difficult to find xe2x80x9coff the shelfxe2x80x9d and are therefore expensive and time-consuming to custom produce. Moreover, optical systems incorporating nested cylindrical lenses for anamorphic image magnification and relay often introduce additional distortion into the image (e.g, coma), since light rays must pass obliquely through orthogonally-active lenses.
Although advantageous from a cost and simplicity standpoint, current FCLs are generally optimized for only one wavelength and thus exhibit significant chromatic aberration. This typically results in a wavelength-dependent axial shift of the focus and a variation in convergence angle to that focus, both of which are detrimental to the process of producing high-quality multiple or full color holograms.
Another issue associated with the image projection optics arises when a three-color image relay is considered. Optical design for fast cylindrical lenses, or any lens, for that matter, is greatly simplified if proper performance is only desired for a single wavelength. This is due to the inherent chromatic dispersion of lens materials (e.g., glass, borosilicates, and fused silica), which causes simple xe2x80x9csingletxe2x80x9d lenses to focus light of different wavelengths in different planes. This phenomena is called chromatic aberration. It is possible to design optical systems that minimize chromatic aberration; however, these systems are typically more complex than their single wavelength counterparts, usually requiring a number of different lenses/materials sometimes cemented in pairs (doublets), or even threes (triplets). Such systems are also less efficient than their monochromatic counterparts, since the necessary inclusion of additional materials and elements produces more absorption and spurious interface reflection of the light passing through that system.
Accordingly, it is desirable to have a hologram producing system where size, cost, and complexity are reduced, while maintaining an efficient system that introduces few additional sources of distortion, and produces high quality holograms.
In accordance with teachings of the present invention, a system and method are disclosed to provide manufacturable, affordable, robust one-step horizontal parallax only holographic stereogram systems for commercial markets. The present invention allows a substantially monochromatic fast cylindrical lens (FCL) to produce substantially the same results as an achromatic FCL.
An objective of the design of such a system is simplicity, efficiency, and cost minimization. Aside from the lasers, some of the most expensive components of such systems are the associated fast cylindrical lens (FCL). By combining simple, inexpensive chromatic corrector optics with image scaling in accordance with teachings of the present invention, a relatively inexpensive FCL can be used, thus avoiding the added cost and complexity of an achromatic FCL. Additionally, incorporation of chromatic corrector optics in accordance with teachings of the present invention, allows for a more efficient system, since it adds fewer optical material volumes and material-to-air surfaces through which light must pass. The present invention can enable use of lower power lasers which will generally reduce the price and increase the robustness of the resulting system.
Accordingly, one aspect of the present invention provides a system for relaying and conditioning color images for use in producing a holographic stereogram. The system includes at least two spatial light modulators and a color combining element for receiving a respective color image from each spatial light modulator. Respective chromatic corrector optics are disposed between each spatial light modulator and the color combining element. A first cylindrical lens is located to receive the color images from the first and second spherical lenses and to project the color images to produce the holographic stereogram.
Another aspect of the present invention provides a system comprising a first projection system, a projection-distortion corrector mechanism, and a second projection system. The first projection system includes optics substantially optimized to project an image generated via a first-frequency light source onto a recording plane. The second projection system projects an image generated via a second-frequency light source onto the recording plane. The second projection system has a substantial duplication of at least a part of the optics substantially optimized to project the image generated via the first-frequency light source onto the recording plane, and the substantial duplication is operably coupled with the projection-distortion corrector mechanism.
In another aspect of the present invention, a method includes compensating for distortion of an image projected onto a recording plane in a projection system. The image is generated via a second-frequency light source and the projection system has optics substantially optimized for a first-frequency light source. The compensating is achieved by operably coupling a projection-distortion correction mechanism with the projection system.